Computational Environment to Semi-Automatically Build a Conceptual Model Represented in OntoUML

Abstract

A conceptual model can be an important instrument to support the software functional requirements elicitation because it promotes better understanding of a domain. However, the representation quality of the conceptual model depends on the expressivity of the language used. OntoUML is a proposed language to solve expressivity problems. Nevertheless, OntoUML models are complicated to build for novice modelers. This study presents an experiment performed in order to semi-automatically build a conceptual model represented in OntoUML. All the experiment steps were executed by a computational environment named ENSURE. The results showed that it is possible to identify 60% of the meaningful concepts.

1. Introduction

more expressive language, it proposes a larger set of constructs that are not easily identified, especially by novice modelers (Guizzardi et al., 2011) .

Motivated by these challenges, this study describes an experiment to build semiautomatically a conceptual model represented by OntoUML. All steps described in the Experiment Method Section are executed by a computational environment called ENSURE (ENvironment to SUpport Requirement Elicitation). One of the main goals of ENSURE is to support the extraction of functional requirements of a domain using a conceptual model represented by OntoUML. This paper is organized as follows: in Section 2, the background of the proposal is outlined. Section 3 presents the method of the experiment, while Section 4 presents the results of the experiment. The final considerations and future works related to the proposal are presented in Section 5.

2. Background

This section presents the main concepts related to this study. The concepts are not exhaustively explained due to space limitation. However, they are discussed enough to understand the experiment executed.

2.1 OntoUML

The OntoUML language proposed by Guizzardi (2005) was motivated by the need for an ontology-based language that would provide the necessary semantics to construct conceptual models with concepts that were faithful to reality. The classes proposed in OntoUML are specializations of the abstract classes of the Unified Foundational Ontology (UFO) and extend the original metamodel of UML.

In this study, only the main constructs that make up the object type category will be presented (Guizzardi et al., 2011) . In this category, constructs are more closely related to the static conceptual modeling of a domain. The Object Type constructs can be Sortal and Non-Sortal. The Sortal constructs provide identity and individualization principles to their instances, while the Non-Sortal constructs do not supply any clear identification principles. The Sortal constructs are classified as Rigid Sortal and AntiRigid Sortal. A Sortal is classified as rigid if it is necessarily applied to all its instances in all possible worlds. A Sortal is said to be anti-rigid if it is not necessarily applied to all its instances. The Rigid Sortal includes the Kind and Subkind categories. A Kind is a Rigid Sortal, and therefore has intrinsic material properties that provide clear identity and individualization principles. The Kind determines existentially independent classes of things or beings and are said to be functional complexes. A Subkind is also a Rigid Sortal that provides the identity principle and has some restrictions established and related to the Kind construct. Every object in a conceptual model must be an instance of only one Kind. There are two sub-categories of Anti-Rigid Sortal: Phases and Roles. In both cases, the instances can change their types without affecting their identity. Whereas during the Phase construct, the changes can take place as a result of changes of intrinsic properties. In the Role construct, the changes take place because of relational properties.

Compared with UML, OntoUML has a larger set of constructs, enabling greater expressivity of conceptual models and avoiding overload and redundancy (Guizzardi, 2005) . Nevertheless, OntoUML is more complex to use than the traditional languages, such as UML, especially for novice modelers (Guizzardi et al., 2011) . One of the difficulties of constructing a model represented in OntoUML is identifying the correct construct for a given concept to be represented. In this sense, it is important to develop automatic or semi-automatic mechanisms that help the domain modeler to identify this concept and its correct construct. A linguistic approach with a semantic focus can be applied to aid comprehension of the concepts to be modeled (Castro, 2010) .

2.2 Semantic types and Disambiguation

Dixon (2005) proposed a semantic organization for words in classes of meaning known as semantic types. In this proposal, semantic types handle nouns, adjectives, and verbs. Generally, in conceptual modeling, nouns are the semantic types that indicate important concepts in a conceptual modeling. The semantic types can be mapped to the constructs of OntoUML (Castro, 2010) and thereby enable semi-automatic support for their identification using Natural Language Processing (NLP). However, one of the challenges of automatic identification of the semantic type is the disambiguation of the term (Castro, 2010; Leão et al., 2013) .

A word can have several meanings and the correct identification of its meaning may depend on the context in which it is used. The task of computationally identifying the meaning of words based on their context is known as Word Sense Disambiguation (WSD) (Pedersen and Kolhatkar, 2009) . Techniques and algorithms for disambiguation are available, such as TargetWord, which is applied only in the case of a target word in a sentence, and the AllWord, which is applied to all words in a sentence. An example of a disambiguation technique is WordNet::SenseRelated (Pedersen and Kolhatkar, 2009) . WordNet:SenseRelate is based on WordNet, which is a lexical base for the English language. This tool performs the disambiguation of a term found in the base and also identifies the corresponding semantic type. Figure 1 illustrates the use of Semantic types and Disambiguation concepts, where an example of “driver” term from WordNet database is presented. The term “driver” can have different meanings that depend on the context and each one can have different semantic type. In the “driver” example, the term can be associated to three semantic types: person, communication, and artifact. Considering the context, the TargetWord algorithm identifies the correct meaning. When the correct meaning is identified, it is possible to retrieve the associated semantic type.

2.3 ENSURE

ENSURE is a computational environment developed to support the execution of tasks related to Software Requirement Engineering. This environment contains in the integration of relevant terms, extraction algorithms, terms disambiguation algorithms, WordNet database, OLED (2015) (OntoUML editor) and others.

This integration and interfaces allow the management of domain texts, identify relevant terms, execute terms disambiguation using WordNet database, build conceptual model, and derive functional requirements of a domain. The main goal of the environment is to support the decision taking in each one of these tasks. The main users comprise students of Requirement Engineering, the novice professionals.

3. Experimental Method

The experiment to build semi-automatically a conceptual model was conducted based on the steps of the method proposed in ( Leão et al., 2013 ; Valaski et al., 2014). The main differences in this experiment are a new heuristic to identify the OntoUML construct, the execution by a computational environment, and the partial building of a conceptual model. Each one of these tasks are executed using the ENSURE.

3.1 Identifying relevant terms

The first step was the selection of the text. In this experiment, the same text applied on Valaski et al. (2014) was used. This decision was taken to facilitate the comparison between the previous and present experiment. The text selected is presented in Table 1 and describes a domain of bus route. The next step was the selection of the relevant terms. The starting point to define the relevant terms is the conceptual model relative to the text. The conceptual model is represented using the ER model (Gemino and Wand, 2005) . Table 2 presents the 32 terms identified as relevant. In the context of this experiment, the terms are called “gold terms”. They were compared with the terms automatically extracted.

The last step was the selection of algorithm to extract the relevant terms. The topia.termextract version 1.1.0, developed by Python (https://pypi.python.org/pypi/topia.termextract/) was used. This tool was chosen because of its satisfactory results (Valaski et al., 2014) and its use is free. To analyze Topia algorithm results, the metrics precision and recall Fawcett, T. (2006 ) were used. There are two ways for people to travel with Voyager. Either passengers can make a reservation on a trip, or passengers can show up at the boarding gate without a reservation and purchase a ticket for an unreserved seat. Passengers with a reservation are assigned a reservation date, whereas, passengers without reservations are assigned a boarding date. The name and addresses of all passengers are collected. Telephone numbers are collected where possible. All bus trips are organized into daily route segments. All daily route segments have both a start time and an end time. Each daily route segment. Voyager organizes is classified as a route segment with a segment number, start town, and finish town. Voyager offers a range of trips, and each trip is made up of one or more route segments. For every trip there is a trip number, start town, and finish town. If the trip is organized around a special event, the event name is also associated with the trip. Each daily route segment that Voyager offers is part of a dally trip. A daily trip is undertaken by one or more bus drivers. The name, address, and employee number of all drivers is collected. Voyager also records information about absent drivers. When a driver is absent. Voyager records the absence start date and the details about the absence. The absent driver provides one or more reasons for being absent and each reason is assigned a detail number and a short description. Voyager also collects information about the buses used for daily trips. Buses have a make, model, and registration number. For buses in use, the average daily kilometers is collected. If a bus requires maintenance, Voyager notes the date on which the bus entered maintenance and records the one or more problems with the bus. Voyager assigns a problem number and a short description for every maintenance problem. Finally, the average cost to repair all problems with a bus in maintenance is also recorded. Absence; Absence Start Date; Address; Average Daily Kilometers, Average Cost to Repair; Boarding Date; Bus; Daily Route Segment; Daily Trips; Date Maintenance; Description; Details; Driver; Employee; End time; Finish Town; Maintenance Problems; Make; Model; Name; Passengers; Problem; Registration number; Reservation Date; Route Segment; Segment; Event name; Start Time; Start Town; Telephone; Trip; Trip Number

3.2 Identifying OntoUML construct

After selecting the relevant terms using Topia algorithm, the following heuristics were applied:

Rule i: For each relevant term (simple or compound), verify if the last word is number, name, or date. If true, the construct suggested must be Datatype. This rule was built because it was observed in previous experiment (Valaski et al., 2014) that these terms in general are not identified in the semantic database. Furthermore, these terms in general are observed to be related to attributes.

Rule ii: For each relevant term, where Rule i is not true, apply the algorithm TargetWord to disambiguate the term. If the TargetWord obtained the term disambiguate, retrieve the associated semantic type. With the semantic type, retrieve the OntoUML construct using the mapping described in Table 3. This mapping was established by partially using the proposal of Castro (2010) . Castro used the Dixon (2005) theory to propose some mapping between semantic types and OntoUML construct.

Rule iii: For each relevant term, where Rules i and ii were not true, apply the following rules: if compound term (two or more words), verify if it is the suggested construct for each word individually. If suggested individually, the construct is either Kind or Relator; suggest the construct Relator. Example: Bus Trips, this term does not exist in the WordNet database. However, the terms bus and trip exist. When the TargetWord algorithm was executed, the construct Kind was identified to the bus term and the construct Relator to the trip term. In this example, rule iii must suggest the construct Relator to the term Bus Trips. Rule iii was also extracted based on the observation of previous experiments. The simple terms were found, but the compound terms were not. This rule is a suggestion to try solving cases where the terms are not found in the WordNet database. It is important to emphasize that despite the application of these three rules, some terms are not suggested by the environment. The obtained results of this step were compared with previous results (Valaski et al., 2014) .

3.3 Building conceptual model represented in OntoUML

Using the relevant terms, where the corresponding constructs were identified, the conceptual model was built. The OLED editor (2015) was used to build the model. In this experiment, the model was limited to represent only the elements without their relationship. This is a challenge to be addressed in future works. A complete model was manually built to compare the results obtained between the manual and automatic processes. The precision and recall metrics were used to calculate the accuracy and completeness of the results.

4. Experiment Results

The results of the experiment are presented according to the steps described in Section 3. All steps are executed automatically by ENSURE.

4.1 Identifying relevant terms

The results presented in Table 4 show that among the 31 terms identified by Topia, 14 terms have exact correspondence with the gold terms, while 17 terms do not have exact correspondence. On the other hand, the results presented in Table 5 show that among the 32 gold terms, 14 terms have exact correspondence with the relevant terms extracted by Topia, while 18 terms do not have exact correspondence. Based on these results, the precision (formula 1) and recall (formula 2) metrics were calculated. To proceed with the calculation, the following auxiliary variables are used: CT (total of correct terms returned by Topia); nCT (total of not correct terms returned by Topia); and CGn (total of gold terms do not returned by Topia).

Precision = CT/(CT + nCT) = 14/(14 + 17) = 0.4516 (1) Recall = CT/(CT + CGn) = 14/(14 + 18) = 0.4375 (2)

The precision metric shows that Topia algorithm has an accuracy of 45.16%, while the recall metric shows that Topia algorithm has a completeness of 43.75%. The results were considered reasonable mainly because only the terms with exact correspondence were considered. On the other hand, if terms with partial correspondence (third column Tables 4 and 5) were also considered, better results were obtained. Topia extracted 27 terms with partial correspondence with gold terms (CT), while only 4 terms (Record; Records information; Unreserved seat) do not have partial correspondence (nCT). Only 9 terms (Absence; Absence start date; Address; Average daily kilometers; Average cost to repair; description; make; model; Start time) from the gold list do not have partial correspondence (CGn). The precision (formula 3) and recall (formula 4) metrics were recalculated. Recall = CT/(CT + CGn) = 27/(27 + 9) = 0.75 (4)

If partial terms are considered to collaborate with the identification of the relevant concepts of a model, Topia had an accuracy of 87.09% and completeness of 75%.

4.2 Identifying OntoUML construct

The heuristic described in Section 3.2 was applied with the list of relevant terms extracted by Topia. Figures 4 and 5 show the execution sequence to identify the construct. Figure 4 shows the XML file created. An XML file is required to execute the TargetWord algorithm described in Section 3.2, rule ii. In this file, the relevant terms are tagged in the original text. The TargetWord algorithm performs the disambiguation using the WordNet database and returns the corresponding semantic type. Figure 5 presents the disambiguation result and the construct suggested according to the mapping proposed in Table 3.

Among the 31 relevant terms extracted by Topia, the environment suggested construct to 28 terms, which comprise about 90% accuracy. Considering these 28 terms, 13 had the construct suggested as Datatype (rule i), 12 had the construct suggested using the disambiguation process (rule ii), and 3 had the construct suggested using semantic type assigned by the simple terms (rule iii). In the experiment described in Valaski et al. (2014) , among the 31 identified relevant terms, only 12 terms had suggested construct, comprising about 40% accuracy. The new heuristic contributed to identify mainly terms associated to Datatype construct. It also contributed to identify the construct of terms not found in the WordNet database, such as Bus Trips, Route Segment, and Maintenance Problems. These terms exemplified situations where the compound terms are not found but the simple terms are found. It is important to state that this experiment only indicates the possibility to explore this kind of association. Other experiments with a diversity of text must be executed to confirm the validation of rule iii.

4.3 Building conceptual model represented in OntoUML

The conceptual model was generated both automatically and partially using the relevant terms list and the construct suggested. The conceptual model was built on OLED editor. Figure 6 shows the results of Figure 5 execution. The automatic identification of the relationship among terms is not yet possible on ENSURE. This is a challenge to be addressed in future work.

The conceptual model in Figure 7 is manually built corresponding to the processed text (bus route) to analyze the result of this step. This model represented only the elements related to Kind, Role, and Relator (12 elements). The ER conceptual model presented in (Gemino and Wand, 2005) was also used to validate the model built. The elements associated to Datatype construct were not presented as they were considered less representative in this experiment. The model in Figure 7 was named as “gold model”.

Considering only elements associated to Kind, Role, and Relator construct, the environment automatically identified 15 elements (Bus, Bus drivers, Bus Trips, Driver, Maintenance, Maintenance Problems, Passengers, Problem, Reservation, Route, Route Segment, Segment, Town, Trip, Voyager). Among of them, nine are present in the gold model (gray elements). Only the terms Bus drivers, Bus Trips, Maintenance, Route, Segment, and Voyager do not have exact correspondence in the gold model. However, all terms, except Voyager, have partial correspondence in the gold model. That is, if the exact concept is not identified, it is believed that the partial concept can help in finding the exact concept. Among the elements represented in the gold model, only three terms were not identified by the environment, namely, Person, Daily Trip, and Daily Route Segment. However, the partial terms Trip and Route Segment were found. Considering these results, the precision (formula 5) and recall (formula 6) metrics are calculated.

Precision = 9/(9+6) = 0.60 (5) Recall = 9/(9+3) = 0.75

(6)

In this context, considering only the more representative elements (Kind, Role, Relator) of the gold model, the environment had an accuracy of 60% and completeness of 75%. The quality and complexity of the text directly influence the accuracy of the results.

5. Conclusion

An experiment was performed to demonstrate the semi-automatically building of a conceptual model represented in OntoUML. The execution was performed through a computational environment called ENSURE. The initial results were considered satisfactory because through a domain text, it was identified 60% of the meaningful concepts. However, a number of challenges need to be addressed to improve the used methods and the environment. Some of these main challenges are: availability of algorithm and tools to process natural language with better results and availability of terms in semantic database to perform disambiguation. Another challenge is to identify automatic relationship among the elements in a conceptual model.

ENSURE is an environment built to promote Requirement Elicitation using a conceptual model represented in OntoUML as support. From the conceptual model, the environment suggests functional requirements of a domain. New implementations are currently executed to improve the building of the conceptual model and the extraction of its functional requirement.

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